Applies To:
  • CitectSCADA 1.00, 1.01, 1.10, 1.11, 2.00, 2.01

It is possible to configure an I/O Server where the Primary I/O Device will use one protocol and the Standby I/O Device will use another protocol. This configuration is not supported by Citect and should not be used. The Citect Compiler does not generate an error message if you configure this setup however it is invalid. For example you may try to configure Citect where the Primary protocol is a TIWAY Card to a Texas 565 PLC and the Standby Protocol is Tiway Direct using Serial port to the same PLC. This configuration is invalid and when the Standby I/O Device becomes active you may get the following error messages: 'Reg Size Too Bit n' or 'Bad data/unit n type', where n is a number. If you don't get these error messages this configuration may appear to work correctly, however it is unstable and may fail to operate correctly in the future. 

The primary and Standby I/O Devices must be the same type of PLC and must use the same protocol to the PLC.